#include <iostream>
#include <cstdio>
#include <queue>
#include <cstring>
using namespace std;
const int N = 1e3 + 5;
const int M = 1e5 + 5;

int head[N], revhead[N], cnt;
int f[N], st[N];
struct Edge{
    int v, w, next;
}edge[M << 1];
struct Node1{
    int idx, dist;
    bool operator < (const Node1& a) const {
        return dist > a.dist;
    }
};
struct Node2{
    int evalue, idx, dist;
    bool operator < (const Node2& a) const {
        return evalue > a.evalue;
    }
};

void add(int array[], int u, int v, int w)
{
    edge[++cnt].v = v;
    edge[cnt].w = w;
    edge[cnt].next = array[u];
    array[u] = cnt;
}

void dijkstra(int s)
{
    memset(f, 0x3f, sizeof(f));
    priority_queue<Node1> heap;
    Node1 start = {s, 0};
    heap.push(start);
    f[s] = 0;
    while (heap.size())
    {
        Node1 cur = heap.top();
        heap.pop();
        if (st[cur.idx]) continue;
        st[cur.idx] = 1;
        for (int i = revhead[cur.idx]; i; i = edge[i].next)
        {
            int v = edge[i].v;
            if (f[v] > cur.dist + edge[i].w)
            {
                f[v] = cur.dist + edge[i].w;
                Node1 next = {v, f[v]};
                heap.push(next);
            }
        }
    }
}

int a_star(int s, int e, int k)
{
    memset(st, 0, sizeof(st));
    priority_queue<Node2> heap;
    Node2 start = {f[s], s, 0};
    heap.push(start);
    while (heap.size())
    {
        Node2 cur = heap.top();
        heap.pop();
        if (st[cur.idx] >= k) continue;
        st[cur.idx]++;
        if (cur.idx == e && st[cur.idx] == k) return cur.dist;
        for (int i = head[cur.idx]; i; i = edge[i].next)
        {
            int v = edge[i].v;
            if (st[v] < k)
            {
                Node2 next = {edge[i].w + cur.dist + f[v], v, edge[i].w + cur.dist};
                heap.push(next);
            }
        }
    }
    return -1;
}

int main()
{
    int n, m;
    scanf("%d %d", &n, &m);
    for (int i = 0; i < m; ++i)
    {
        int u, v, w;
        scanf("%d %d %d", &u, &v, &w);
        add(head, u, v, w);
        add(revhead, v, u, w);
    }
    int s, e, k;
    scanf("%d %d %d", &s, &e, &k);
    if (s == e) k++;
    dijkstra(e);
//  for (int i = 1; i <= n; ++i) cout << f[i] << " ";
    printf("%d", a_star(s, e, k));
    return 0;
}